The present invention relates to a knocking detecting device for an internal combustion engine and a method therefor, and in particular, relates to a knocking detecting device suitable for a gasoline engine used for an automotive vehicle and a method therefore.
When knocking is generated in an engine, a vibration having characteristic resonance frequency components is generated. Therefore, a the occurrence of knocking is judged by detecting this vibration.
In actual detection of the presence and absence of knocking, it is necessary to separate the vibration induced by knocking from background vibrations having no relation to knocking among engine vibrations detected by a vibration sensor.
Therefore, in conventional knocking detecting devices, such as disclosed in JP-A-58-45520(1983), predetermined resonance frequency components in the range of 5.about.12 KH.sub.z are separated produced by the output signal from a vibration sensor using a band pass filter and the presence and absence of knocking is judged by a determination of whether or not an integrated value of the output form the band pass filter exceeds a predetermined level.
Further, in the above exemplified knocking detecting device, the integration of the resonance frequency components was performed by an analog circuit to detect presence and absence of the knocking.
In the above exemplified conventional knocking detecting devices, influences caused by vibrations other than knocking vibration contained in the output signal from the vibration sensor, such as seating vibration by valves and sliding vibration by pistons, are not sufficiently taken into account. As a result, the conventional knocking detection devices are susceptible to noises during a high speed engine rotation so that there was a problem in the operation of such devices with regard to an accurate knocking detection because of a poor detection sensitivity.
Further, in the conventional knocking detection devices, methods of providing an accurate processing of the output signals from the vibration sensor, such as with Fast Fourier Transform, were not taken into account for judging generation of knocking and therefore, sufficient use could not be made of valuable information contained in the output signal from the vibration sensor with the result that there was a problem that an accurate judgement of the presence and absence of knocking could not be achieved.
Still further, the conventional knocking detecting devices have not taken into account the fact that the vibration caused by knocking is not necessarily distributed over the entire period of one explosion stroke; and so vibration signals over a substantial period of one explosion stroke, which includes vibrations when no knocking has occurred were used for knocking judgement. As a result during a heavy load and high speed operation of an internal combustion engine in which the level of noise vibration increases, there was a problem that detection of knocking vibration was difficult, thereby rendering the judgement of knocking impossible. Thus, it has been difficult to accurately detect knocking at an engine rotation speed more than 3000 rpm and in an engine power zone.